(a) Field of the Invention
The present invention relates to a laser welding method for metal sheets. More particularly, the present invention relates to laser welding method for metal sheets wherein a low heat input laser beam is irradiated to a weld zone with a uniform welding pattern of a zigzag shape, with a constant pitch, and with a constant welding speed, thereby enhancing joinability of the weld zone.
(b) Description of the Related Art
Generally, in an assembling process of a vehicle, spot welding is widely used, and arc welding and laser welding are used when the spot welding is not appropriate.
Gas metal arc welding (GMAW), representing arc welding, is a semi-automatic or automatic arc welding process in which a continuous and consumable wire electrode as a filler metal and a shielding gas are fed through a welding gun to a base metal for forming an arc between the wire and the base metal.
In the gas metal arc welding method, the continuously fed wire is melted by the arc and forms a metal vapor or globule and the base metal is melted to be a molten weld pool. The fusion zone is separated from the atmosphere by the shield gas supplied from a gas nozzle, and gas metal arc welding, according to the kind of shield gas, is classified as metal inert gas (MIG) welding using an inert gas such as Ar and CO2, arc welding using CO2, and metal active gas (MAG) welding using a mixture of Ar and CO2.
The gas metal arc welding generally uses a relatively small diameter electrode wire (0.9-1.6 mm diameter) so that it has a relatively higher deposition rate and is more efficient than shielded metal arc welding (SMAW), consumes relatively less welding materials, and may achieve welding efficiency of more than 95%. Also, automation using a welding robot and so on may be easily achieved and welding productivity may be enhanced.
The gas metal arc welding equipment is relatively more complex than that of the shielded metal arc welding (SMAW) so a breakdown or failure may frequently occur, and it is relatively much more expensive. Gas metal arc welding also generates a large amount of spatter that adheres to the base metal so as to deteriorate appearance. Also, when the spatter adheres to the nozzle, it may disturb the supply of shield gas so as to deteriorate welding quality. Further, the gas metal arc welding process may not be used when it is difficult to approach the weld zone with the welding gun.
Laser welding has a relatively high welding speed, a short welding cycle, small heat input, a small heat affected zone (HAZ), little deformation, and so on, so the laser welding has been increasingly widely used in industry while replacing spot welding and arc welding. In laser welding, keyhole welding using energy reflection and absorption in a focal region of a laser beam has been widely used, and the distance of the keyhole welding region from a focus is within 2 mm.
That is, according to keyhole welding that is performed at the keyhole welding region, electromagnetic waves of the laser beam collide with the material surface at a focal point where the laser beam is converged, collision energy is transformed into heat energy, and a keyhole effect occurs. Such keyhole effect means a state where welding is performed when a plurality of small holes are made in a melted pool by vapor pressure.
However, conventional laser welding, particularly keyhole welding, uses high power so as to penetrate a weld zone and forming a crater along a welding line so that good weld quality, such as with arc welding, may not be obtained.
Thus, laser welding is under investigation for obtaining good weld quality, such as with arc welding, which may achieve autogenous welding without feeding wire.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.